1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive porcelain composition, a piezoelectric/electrostrictive ceramic, and a piezoelectric/electrostrictive film type device. In more detail, the present invention relates to a piezoelectric/electrostrictive porcelain composition capable of manufacturing even at a comparatively low firing temperature a piezoelectric/electrostrictive ceramic or a piezoelectric/electrostrictive portion which is dense, superior in crystallinity, and has superior piezoelectric/electrostrictive characteristic and durability even under conditions of high temperature with high humidity. Furthermore, the present invention relates to a piezoelectric/electrostrictive ceramic which is dense, superior in crystallinity, and has superior piezoelectric/electrostrictive characteristic and durability even under conditions of high temperature with high humidity. The present invention also relates to a piezoelectric/electrostrictive device which is dense, superior in crystallinity, and has superior piezoelectric/electrostrictive characteristic and durability even under conditions of high temperature with high humidity.
2. Description of the Related Art
Piezoelectric/electrostrictive devices have heretofore been known as devices capable of controlling minute displacements in a submicron order. Especially, a piezoelectric/electrostrictive film type device comprising: a piezoelectric/electrostrictive portion made of a piezoelectric/electrostrictive porcelain composition; and an electrode portion to which a voltage is applied, laminated on a substrate constituted of a ceramic is suitable for the control of the minute displacement, and further has superior characteristics such as high electromechanical conversion efficiency, high-speed response, high durability, and low power consumption. These piezoelectric/electrostrictive devices are used in various applications such as piezoelectric pressure sensor, prove-transferring mechanism in scanning tunnel microscope, rectilinear guide mechanism in ultra-precision processing apparatus, servo valve for hydraulic control, head of VTR device, pixel constituting flat panel type image display device, and head of ink jet printer, and the like.
Moreover, the piezoelectric/electrostrictive porcelain composition constituting the piezoelectric/electrostrictive portion has also been various studied. For example, a Pb(Mg1/3Nb2/3)O3—PbTiO3—PbZrO3 ternary system solid solution composition, or a piezoelectric/electrostrictive porcelain composition in which a part of Pb of the composition is substituted with Sr, La or the like has been described (see, e.g., JPB-44-17103 and JP-B-45-8145). It has been expected that a piezoelectric/electrostrictive device having a superior piezoelectric/electrostrictive characteristic (e.g., a piezoelectric d constant) is obtained from the piezoelectric/electrostrictive portion which is a most important portion for determining the piezoelectric/electrostrictive characteristic of the piezoelectric/electrostrictive device.
However, in a conventional piezoelectric/electrostrictive device, when a high electric field is applied on severe use conditions such as a high-temperature condition at 35° C. or more after installation, or a high-humidity condition at 80% RH or more, micro cracks are sometimes generated in the piezoelectric/electrostrictive portion. Therefore, especially when the number of repeating times of the application of the high electric field is large, the characteristic of a piezoelectric/electrostrictive material lowers in some case, and there has been a problem in durability.
On the other hand, when the piezoelectric/electrostrictive portion of the piezoelectric/electrostrictive device is constituted in such a manner as to be denser, superior in crystallinity, and indicate a high piezoelectric/electrostrictive characteristic, the piezoelectric/electrostrictive material (e.g., PZT-based composition) which is a raw material needs to be, fired at 1200° C. or more. Therefore, in addition to a problem that energy costs are high, there have been problems that it is difficult to use an Ag electrode or an Ag—Pd electrode having a comparatively low melting point, an electrode containing expensive Pt has to be used in many cases, and versatility is insufficient.
To solve the problems, there have been made some attempts to add glasses such as lead borosilicate glass, silicate glass, and borosilicate glass to the piezoelectric/electrostrictive material, and form and densify the piezoelectric/electrostrictive portion or a piezoelectric/electrostrictive ceramic at a lower firing temperature (see, e.g., Japanese Patent No. 3236641 and BP-A-2161647). However, in pursuit of the firing at the low temperature, there are problems that the piezoelectric/electrostrictive characteristic largely drops because a glass amount is large. The durability of the piezoelectric/electrostrictive ceramic or the like has not been evaluated in the present situations. Since the glass and the piezoelectric/electrostrictive material have high reactivity, there have been problems that the obtained piezoelectric/electrostrictive portion or piezoelectric/electrostrictive ceramic does not necessarily have desired composition, and the piezoelectric/electrostrictive characteristic drops.